Japan Utility Model Publication (Unexamined Application) No. 5-90897 discloses the following art as a conventional example of an inverter circuit driving a driven unit using two step-up transformers.
That is, as shown in FIG. 13, the conventional example describes an inverter circuit 308 comprising: an inverter circuit 304a having a step-up transformer 301a having a primary winding 309a, a secondary winding 305a and a feedback winding 306, and a pair of transistors 302a and 303a for push-pull driving; and another inverter circuit 304b having a step-up transformer 301b having a primary winding 309b and a secondary winding 305b, and a pair of transistors 302b and 303b for push-pull driving, wherein the feedback winding 306 of step-up transformer 301a is also used in self-excited oscillation of the other inverter circuit 304b. By means of the inverter circuit 308, alternating voltages that are in opposite phase to each other are applied between secondary winding 305a and secondary winding 305b that are connected to both ends of a fluorescent tube 307.
Inverter circuit 308 of the above conventional example uses only the feedback winding of step-up transformer 301a comprised by one inverter circuit 304a to attempt to reverse the phase relationship for the phases of the output from the secondary windings of the step-up transformers on both sides, and the feedback winding of the other step-up transformer is not used. In this configuration, the phases of voltages output from the secondary windings 305a and 305b of the two inverter circuits 304a and 304b cannot be stabilized to reverse the phase relationship thereof, and thus driving becomes imbalanced and both ends of fluorescent tube 307 cannot be lit to an equal level of brightness.
More specifically, when configuring the controlling inverter circuits according to the above conventional art so that the output voltages of inverter circuits connected to both ends of a driven unit are of opposite phases, because the oscillation frequencies of inverter 304a and inverter 304b are different to each other, a phase difference is generated and oscillation becomes unstable. Accordingly, a problem arises whereby potential at both ends of the driven unit cannot be stabilized to reverse the phase relationship thereof.
With the foregoing problem in view, it is an object of the present invention to provide an inverter circuit that stabilizes the potentials at both ends of a driven unit to reverse the phase relationship thereof, and improves the power efficiency of the driven unit.
A unit driven using this type of inverter circuit may be a fluorescent tube, as also described in the conventional example. For a fluorescent tube it is desirable that the brightness thereof be uniform from one end of the tube to the other end. However, when a fluorescent tube is lit using the above conventional art, the phases at both ends do not stabilize and the phase relationship cannot be reversed, and as mentioned above, a problem thus arises that brightness at both ends does not become constant.
Therefore, with the foregoing problem in view, another object of the present invention is to provide a fluorescent tube driving apparatus that stabilizes the potentials applied at both ends of a fluorescent tube to reverse the phase relationship thereof, to thereby redress an imbalance in the luminescent brightness of the fluorescent tube and emit light almost uniformly across the entire tube, and furthermore, improve the luminous efficiency of the fluorescent tube.
A backlight is used as a lighting apparatus for a display apparatus such as, for example, a translucent liquid crystal display, and a fluorescent tube is mainly used as the lighting source of the backlight. In such type of backlight, a uniform level of brightness is required throughout the entire display to prevent inconsistencies in brightness being generated on the display screen. However, when driving a backlight using the conventional art, since it is not possible to stabilize the voltages at both ends of a fluorescent tube to reverse the phase relationship thereof, the brightness at both end sides does not become constant and it is difficult to obtain uniform brightness across the entire display.
Therefore, with the foregoing problem in view, it is a further object of the present invention to provide a backlight apparatus that can stabilize the potentials applied at both ends of a fluorescent tube to reverse the phase relationship thereof, to thereby redress imbalances in luminescent brightness at both ends of the fluorescent tube, and which is capable of having an irradiance distribution of uniform brightness throughout an entire display, and furthermore, high luminous efficiency.
Further, for a liquid crystal display, it is required that the entire display screen be stabilized to designate gradation levels to provide fine image quality. However, a problem exists whereby it is difficult to provide fine image quality unless the brightness of a backlight employed as the light source of the liquid crystal display is constant over the entire display.
Therefore, with the foregoing problem in view, it is a further object of the present invention to provide a liquid crystal display wherein potentials applied at both ends of a fluorescent tube used in a backlight of the liquid crystal display are stabilized to reverse the phase relationship thereof, to thereby redress imbalances in luminescent brightness at both ends of the fluorescent tube to obtain uniform planar luminescence over the entire display, and based thereon, provide fine image quality and furthermore, high luminous efficiency.